A new drug developed to target sexual impotence has sent men flocking to pharmacies and doctors' surgeries all over the United States.

Viagra has been prescribed to 40,000 men in the first three weeks it has been on sale in the US.

British men are also eager to get their hands on the pill, with the British Impotence Association reporting an average 100 calls and 100 letters each day enquiring about Viagra. The drug is expected to go on sale in Europe later this year.

The light-blue, diamond-shaped Viagra tablets are being offered for sale over the Internet at a cost of $105 for 10.

Doctors in the UK have warned that the pills are not suitable for everyone and should only be taken if prescribed.

Up to 40% of men affected

Up to 40% of men are believed to suffer from impotence by the age of 40.

The drug was originally developed to improve blood supply to the heart in angina sufferers. It has now been adapted to facilitiate the flow of blood to the penis necessary to sustain an erection.

By inhibiting the phosphodiesterase 5 (PDE5) enzyme, which is found mainly in the penis, Viagra allows the chemical produced during sexual stimulation, cyclic GMP, to persist.

The longer cyclic GMP persists, the better the chance for increased blood flow.
 

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